Hydroforming with hydrocracking of recycle paraffins



United States Patent HYDROFORMING WITH HYDROCRACKING OF RECYCLE PARAFFINS Charles E. Hemminger, Westfield, N.J., and Donald Dunwody Dunlop, Baton Rouge, La, assignors to Esso Research and Engineering Company, a corporation of Delaware Application December 14, 1955, Serial No. 552,996

1 Claim. ((1208-66) The present invention relates to improvements in the hydroforming of naphthas. More particularly it relates to a process for obtaining improved yields of hydroformate of satisfactory octane number and volatility.

Hydroforming is defined as an operation in which a petroleum naphtha is contacted at elevated temperatures and pressures and in the presence of a recycled hydrogen-containing gas with a solid catalytic material under conditions such that there is no net consumption of hydrogen. Hydroforming processes are well known at this time and the basic operation of the hydroformer is no part of this invention, e.g. see Petroleum Processing, August 1955, pages 1170 through 1196.

Usually the normally liquid feed stock boils substantially within the range of from about 150 to 430 F. and more particularly 200 to 350 F. The light ends, i.e., the material boiling from about to 200 F., are not subjected to this reaction, for the reason that the virgin naphtha light ends have a fairly good octane rating. The feed or charging stock to the hydroforming reactor can be a virgin naphtha, a cracked naphtha, a Fischer-Tropsch naphtha, a mixture of these, or the like.

Hydroforming operations are ordinarily carried out in the presence of hydrogen or hydrogen-rich recycle gas at temperatures of 750 'to 1150 F., in the pressure range of about 50 to 1000 pounds per square inch, and in contact with hydroforming catalysts.

The chemical reactions involved in the hydroforming process include dehydrogenation of naphthenes to the corresponding aromatics, isomerization of straight chain parafiins to form branched chain paraflins, isomerization of cyclic compounds such as ethylcyclopentane to form methylcyclohexane, and some aromatization, dealkylation and hydrocracking of paraflins. In a hydroforming operation which is conducted efiiciently it is possible with the use of a proper catalyst and proper conditions of operation to hydroform a virgin naphtha having an octane number of about 50 to a hydroformate having an octane number of from 95 to 98 and obtain yields of C hydrocarbons as high as 85%.

Platinum has come into ever increasing use in hydroforming because of the high activity of this catalyst for conversion of naphthenes to aromatics. This high production of aromatics results in a hydroformate having a volatility less than desired. A segregation of the hydroformate to include only the fraction in the satisfactory volatility, i.e., boiling point range, results in yield diminution. s

This invention relates to a procedure for the progluetion of high octane gasoline having increased volatility. The present invention comprises separating the C and lower hydrocarbon fraction from the C and higher fraction by distillation and feeding the higher boiling material to a hydrodealkylation unit where the side chains are cracked to produce C and C aromatics. These C and C aromatics can have unsaturated side chains and ice 2 all or a part, i.e., a portion, are recycled to a hydrofiner to s tu the s de chains and. th r by mp o h lead susceptibility.

The hydrofining, reforming and hydrodealkylation steps are conventional and are not claimed per se.

The C and lower fraction contains parafiins, naphthenes and aromatics, whereas the C and higher fraction contains predominantly, i.e., at least 70 wt. percent aromatics. The separation of the two fractions is easily accomplished by distillation as at atmospheric pressure, the C fraction boils typically in the range of 230 to 290 F., whereas the C fraction boils typically in the range of 290 to 350 F.

This invention will be better understood by reference to the following example and discussion of the flow diagram shown in the drawing.

In the drawing fresh feed at a temperature of .650 F. is fed through line 1 to catalytic hydrofiner 2, although the fresh feed can bypass it. The feed is hydrofined at 650 F. over a fixed bed of cobalt molybdate on alumina catalyst. Other hydrofining catalysts can be employed. H 8 and recycle gas are taken off through line 3, after passing through a separating means. Hydrogen for the hydrofining enters hydrofiner 2 through lines 26 and 1.

The hydrofined product after separation from the H 8 and recycle gas is then sent through line 4 to furnace 5 where it is heated to a temperature of 925 F. along with recycle gas from line 25- The aseou m e is fed through line 6 to reactor 7. The naphtha is hydroformed over a fixed bed platinum on alumina catalyst at 925 F. The total mixture is discharged through lin 8 to furnace 9 where it is again heated to reaction temperatures, e.g. 925 F., and then discharged via line 1 .0 to second stage hydroforming rector 11. Several stages of reactors can be employed. The hydroformate together with recycle gas is discharged through line 12 to distillation column 13.

In distillation column 13 the C and higher fractions leave through line 17 and are thus separated from the C and lighter fractions. Recycle gas is taken overhead through line 16 and the C s through line 14, the C to C s through line 15 for blending.

The recycle gas from line 16 and C,}- from line 17 are sent to hydrodealkylater 19. The temperature is bought up to 1000 F. and at a pressure of 500 p.s.i., the aromatics are cracked to C-fs and C s. Polymer bottoms from line 18 can be discharged from the system or sent to the hydrodealkylater.

The reaction mixture is sent through line 20 to distillation column 21. The recycle gas is sent through line 28, line 24, line 26, and line 1 to hydrofiner 2. The cracked aromatic fraction is also sent to the hydrofiner through lines 23 and 1. Tar is discharged through line 22.

The process of this invention is applicable to fixed or fluid bed hydroforming preferably with noble metal catalysts. Suitable catalysts thus include the noble metals such as platinum and palladium, group VI metal oxides, such as molybdenum oxide, chromium oxide or tungsten oxide, or mixtures thereof upon a carrier such as activated olumina, zinc aluminate spine], or the like. The catalysts contain about 0.01 to 2.0 weight percent platinum, about 5 to '15 weight percent molybdenum oxide, orfrom about 10 to 40 weight percent chromium oxide upon a suitable carrier. If desired, minor amounts of stabilizers and promoters such as silica, calcium oxide, ceria or potassia can be included in the catalyst. The catalyst particles are, for the most part, between 200 and 400 mesh in size, or about 0-200 microns in diameter, with a major proportion between 20 and microns in fluidized operation.

In order to explain the process more tully, the following conditions of operation of various components are set forth below and in the examples.

Conditions in hydroformers Preferred Broad Range Range Inlet Temperature, F 900-950 875-975 Pressure, p.s.i.g 250-500 100-700 On. it. of recycled gas fed/bbl. of oil. 2, 000-10, 000 Concentration of H, in recycle gas 60-90 50-95 Conditions in hydrodealkylaiion unit The advantages of the process of this invention are demonstrated in the following examples of low and high severity operations.

Columns I under each are figures for conventional hydroforming.

Columns IA include the additional step of distilling to obtain a product that meets volatility specifications.

Columns 1B under each includes conventional hydroforming plus hydrodealkylation as taught in this invention.

The figures are as follows:

4 These results show: (1) Hydroforming alone (I) gives a product of insuflicient volatility, i.e., does not meet the requirement of about 90 vol. percent boiling at 302 F.

5 (2) Straight distillation of the hydroformate (IA) results in a large loss in yield and octane number. The

loss of the high boiling aromatics contributes to this.

(3) The process of this invention (IB) gives only a slight diminution in octane number over (I) but a 10 marked increase in yield meeting volatility specifications, e.g., 81.2. vol. percent versus 65.4 vol. percent for low severity operations and 75.9 vol. percent versus 56.3 vol. percent for high severity operations.

It is to be understood that this invention is not limited 15 to the specific examples, which have been offered merely as illustrations, and that modifications may be made without departing from the spirit of this invention.

What is claimed is:

A combination process wherein a naphtha feed stock containing both naphthenes and aliphatic hydrocarbons is first contacted with hydrofining catalyst and hydrogen under hydrofining conditions in order to remove sulfur, thereafter the hydrofining feed stock is contacted with a platinum hydroforming catalyst in the presence of hydrogen in a plurality of stages maintained under hydroforming conditions, thereafter the product obtained by hydroforming is subjected to a first distillation stage wherein the C to C hydrocarbons are recovered for gasoline blending purposes and the C s and higher hydrocarbons are delivered to a hydrodealkylation stage maintained under hydrodealkylation conditions where the C s and higher hydrocarbons are converted to C and C aromatic hydrocarbons, thereafter the product of hydrodealkylation is subjected to a second distillation step to remove tar bottoms and the C and C hydrocarbons are recycled to the fresh feed inlet where olefins present are hydrogenated, the result of the process being the formation of a gasoline blending stock which has a volatility such that about 90 volume percent boils at 302 F. due to the presence of a large preponderance of C and C aromatic hydrocarbons, possessing a high octane number and also possessing improved lead susceptibility.

Low Severity High Severity Case IA 113 I IA 13 Operation Hydro- Hydro- Hydro- Hydro- Hydroformlng forming forming forming forming Dist. Dealky. Dist. Dealky.

RON 86. 6 78. 5 86. 2 98. 9 96. 6 98. 5 .Gt-h V01. Percent.. 88. 6 65. 4 81. 2 80. 7 56. 3 75. 9

Fraction Boiling Product Composition, Vol. Percent Range, "F

References Cited in the file of this patent UNITED STATES PATENTS 2,671,754 De Russet et al. Mar. 9, 1954 2,697,684 Hemminger et al. Dec. 21, 1954 2,780,661 Hemminger et a1. Feb. 5, 1957 

